1. Field of the Invention
The present invention relates to telecommunication systems especially wireless systems, wireless transmitters and wireless receivers, especially those using the Bluetooth standard. The present invention also relates to semiconductor integrated circuits that implement a wireless receiver and/or a wireless transmitter especially those using the Bluetooth standard, as well as software for implementing the transmitter and/or receiver.
2. Technical Background
The Bluetooth wireless interface, introduced by the Bluetooth Special Interest Group (Ericsson, Nokia, IBM, Toshiba and Intel) in 1998, is designed to be a low-cost, low-power and short-range cable replacement.
Version 2.0+EDR of the Bluetooth standards introduces an Enhanced Data Rate (EDR) operation. The EDR standard is an improvement over the Basic Rate standard. New modulation schemes based on M-state phase modulation (M greater than 2) are proposed: π/4-DQPSK and 8DPSK, as well as the conventional GFSK. The bandwidth of the channel is 1 MHz.
The unit establishing a connection is called a master. The master unit communicates with slave units. The master unit uses a free-running clock to periodically transmit in every second slot and poll/select one of the slaves in a piconet by implicitly assigning the next slot for the transmission. There are two types of links:                synchronous connection oriented (SCO)        asynchronous connection-less (ACL)The SCO links provide 64 kbit/s service data rate with stringent timing requirements and can be used for constant bit rate real-time services such as voice and video. Up to three SCO links can be established at the same time. The ACL links are packet-oriented and can be used for efficient data transfer for non-time-sensitive data services.        
One of the distortion problems that needs to be compensated in a wireless receiver such as a Bluetooth receiver using EDR is carrier frequency offset. Frequency offset compensation for a receiver without M-state phase modulation (M greater than 2) is disclosed in U.S. Pat. No. 6,703,896 and makes use of monitoring the vector product of adjacent digitized signals. Although this type of frequency offset works well when the number of constellation points is low, the introduction of more complex modulation schemes means that frequency offset has a more serious effect, e.g. on bit errors for long packets in 3 Mbps EDR (3-DH5 packets).
U.S. Pat. No. 5,561,665 describes a frequency offset compensation technique using a vector product and a correlator. The correlator output is compared with a predetermined correlation threshold value and based on that an estimate of the offset is made. Determining an optimum predetermined correlation threshold suitable for all reception conditions can be difficult.
It is also known for frequency offset compensation to apply a rotation directly to digitized complex signals. Compensating directly on the signal can bring degradation to the overall performance and an increase in complexity. The received signal must be rotated and de-rotated, such multiplications being very costly as far as implementation cost goes. Degradation can occur as such rotations on the demodulated signals always bring along approximations which introduce errors.